1. Field of the Invention
The present invention relates to magnetic disk drives and more particularly to read/write transducers utilizing magnetoresistive read sensors protected against electrostatic discharge by semiconducting circuits elements integrated in a layer of silicon attached to a hard, insulating substrate, and further having a hard air bearing surface.
2. Description of the Related Art
Magnetic head disk drive systems have been widely accepted in the computer industry as a cost effective form of data storage. In a magnetic disk drive system, a magnetic recording medium in the form of a disk rotates at high speed while a magnetic read/write transducer, referred to as a magnetic head, xe2x80x9cfliesxe2x80x9d slightly above the surface of the rotating disk. The magnetic disk is rotated by means of a spindle drive motor. The magnetic head is attached to or formed integrally with a xe2x80x9csliderxe2x80x9d which is suspended over the disk on a spring-loaded support arm known as the actuator arm. As the magnetic disk rotates at operating speed, the moving air generated by the rotating disk in conjunction with the physical design of the slider lifts the magnetic head, allowing it to glide or xe2x80x9cflyxe2x80x9d slightly above and over the disk surface on a cushion of air, referred to as an air bearing. The flying height of the magnetic head over the disk surface is typically only a few microinches or less and is primarily a function of disk rotation, the aerodynamic properties of the slider assembly and the force exerted by the spring-loaded actuator arm.
Magnetoresistive sensors, also referred to as xe2x80x9cMR heads,xe2x80x9d are particularly useful as read elements in magnetic transducers, especially at high data recording densities. The MR sensor provides a higher output signal than an inductive read head. This higher output signal results in a higher signal-to-noise ratio for the recording channel and allows higher areal density of recorded data on a magnetic disk surface.
MR heads are typically fabricated on a ceramic substrate of alumina-TiC. However, the ever decreasing cross-sectional area of MR heads, as a result of both film thickness and stripe height reductions, has resulted in increased electrostatic discharge (ESD) sensitivity. Spin valve materials have an additional reversible failure mode when subjected to an electrostatic discharge: underpinning of the pinned layer due to the low blocking temperature of the antiferromagnet.
Static charges may be produced by the presence of certain materials, such as plastics, during manufacture and subsequent handling of the heads, for example. These charges arc across the edge of the insulating layer between the magnetic pole tips and adjacent conductive layers which are exposed and positioned adjacent to the transducing gap at the slider air bearing surface facing the recording medium. This discharge causes erosion of the pole tips and degradation of the transducer in reading and writing data.
As described above, when an MR sensor is exposed to ESD, or even a voltage or current input larger than that intended under normal operating conditions, referred to as electrical overstress or EOS, the MR sensor and other parts of the head may be damaged. This sensitivity to electrical damage is particularly severe for MR read sensors because of their relatively small physical size. For example, an MR sensor used for extremely high recording densities will have a cross-section of 100 Angstroms (A) by 1.0 micrometers (um) or smaller. Discharge of voltages of only a few volts through such a physically small sensor, behaving like a resistor, is sufficient to produce currents capable of severely damaging or completely destroying the MR sensor. The nature of the damage which may be experienced by an MR sensor varies significantly, including complete destruction of the sensor via melting and evaporation, contamination of the air bearing surface, generation of shorts via electrical breakdown, and milder forms of damage in which the head performance may be degraded. This type of damage to the MR head has been found to occur during both processing and operational use, and poses a serious problem in the manufacturing and handling of magnetic heads incorporating MR read sensors.
Electrostatic discharge (ESD) problems associated with the thin film inductive read/write heads are well documented and several solutions have been proposed. Elser et al. U.S. Pat. No. 4,317,149 discloses an inductive head having short discharge paths formed by the deposition of conductive material in recesses formed in an insulating layer so that the static electric discharge will occur in areas displaced from the critical pole tip and gap area at the slider air bearing surface. Schwartz et al. U.S. Pat. No. 4,800,454 discloses an inductive head assembly wherein the magnetic pole piece and the inductive coil winding are coupled to the slider to allow discharge of any static electric charges which may build up. The winding is connected to the slider body via a diode with high forward and reverse voltage drops, or through a fusible link.
U.S. Pat. No. 5,465,186 describes an approach for protecting a magnetic read/write transducer from the effects of electrical overstress and electrostatic discharge during the manufacture and assembly of a magnetic storage system. The conductive leads of a magnetoresistive (MR) sensor element are shorted together to provide a low resistance, conductive path that bypasses the MR element and minimizes electrical current through the MR sensing element during discharge of static electrical charge. The MR sensor lead terminal pads are shorted together by soldering. The other transducer elements such as the MR magnetic shields, the inductive coil and the inductive magnetic yoke structure may also be shorted to the MR sensor leads by soldering the lead terminal pads together at the slider surface. Alternatively, a twisted conductor pair may be used to short the MR terminals together. Remotely located protective devices, such as reversed diode pairs, can also be connected across the MR sensor element using the twisted pair. The short is removed prior to placing the MR head into operation in the magnetic storage system.
U.S. Pat. No. 5,491,605 describes a scheme for protecting a magnetic read/write transducer from EOS and ESD. The elements of the MR and inductive heads are shorted together and to the slider substrate to provide a low resistance, conductive path that bypasses the MR sensor element and minimizes current through the MR element during discharge of electrostatic charge. The MR sensor element, the MR conductive leads, the MR magnetic shield elements and inductive pole tips exposed at the slider air bearing surface are shorted together and to the slider substrate by a layer of conductive material, such as tungsten, formed over the slider air bearing surface. The conductive layer shorts the head elements together and to the slider substrate, thus protecting the head against ESD/EOS damage during subsequent handling and assembly. The conductive layer is removed by wet etching prior to placing the magnetic head into operation in a magnetic storage system.
One limitation of the ESD and EOS protection schemes described above is that after removal of the soldered shorts or conductive layer, the head assembly again becomes vulnerable to EDS/EOS damage while subjected to further manufacturing processes and later in operation. Further, the removal of such shorts and/or conductive layers requires an additional manufacturing step which may cause damage to the heads.
Diodes have been shown to provide increased ESD protection without adversely affecting the testability of an MR head in various processing steps. Furthermore, if the capacitance of the forward biased diode can be kept to a minimum, they have also been shown to have no appreciable affect on the performance of the MR head in the file. However, the only kinds of diodes that can be fabricated on an alumina-TiC substrate are known as xe2x80x9cthin film diodes,xe2x80x9d and their properties are not well understood.
Silicon is a commonly available, low cost material which supports well established p-n junction diode processes. P-n junction diodes fabricated on silicon have capacitances that are proportional to the forward bias current and the carrier recombination time. Since ESD protection is proportional to forward bias current, lower carrier recombination time is the only parameter that reduces the capacitance for a given level of ESD protection. Silicon has a lower hardness than alumina-TiC, and is therefore, easier to scratch than alumina-TiC. Therefore an MR head having an exposed silicon surface would result in inferior head-disk interface performance. Further, the yield strength of silicon is lower than that of alumina-TiC. Therefore, MR heads incorporating silicon structures would tend to break more easily in row form while being handled during the various manufacturing steps to which they would be subjected. Furthermore, overcoat materials, such as silicon dioxide (SiO2) that are known to be compatible with a silicon substrate in air bearing patterning as they can be reactive ion etched or ion-milled at similar rates, have been observed to protrude above a silicon substrate when the air bearing surface is lapped. Such protrusions can result in hard disk contact, which can produce scratches on the surface of the disk.
A need therefore exists for providing an MR read/write head assembly with ESD/EOS protection that is permanently integrated into the MR head assembly in a cost effective manner using well known manufacturing techniques.
A further need exists for an MR head formed on a substrate having a hardness and yield strength that is comparable to alumina-TiC that will support the formation of basic solid-state type diodes.
Yet still another need exists for an MR head made from materials which are compatible with standard overcoat materials, where all such materials have similar lapping rates.
The present invention provides a magnetoresistive read/inductive write magnetic head assembly formed on a hard insulating substrate and having electrostatic discharge protection. The assembly comprises: a hard electrically insulating substrate, preferably formed of sapphire or alumina-TiC; multiple alumina layers formed over the substrate; a magnetoresistive read/inductive write head positioned between the alumina layers; a silicon layer supported by the substrate; and a semiconducting circuit integrated into the silicon layer and interconnected with said magnetoresistive read/write inductive write head which provides a short circuit path to absorb electrostatic discharge during manufacture of the assembly and in subsequent operation. The silicon layer may be epitaxially grown on the sapphire, or bonded to alumina-TiC. The hard insulating substrate and alumina layers provide the assembly with a hard air bearing surface having generally uniform lapping and etching characteristics, and therefore, excellent durability.
In another aspect of the invention, the assembly may comprise a hard insulating substrate, multiple alumina layers formed over the substrate; and a magnetoresistive read/inductive write head positioned between the alumina layers to provide the assembly with a hard air bearing surface having improved durability. Such improved durability facilitates handling and processing of the assembly during manufacture by reducing the risk of damage.
The invention may also be characterized as a method for manufacturing a magnetoresistive read/inductive write magnetic head assembly having electrostatic discharge protection and which is formed on a hard insulating substrate. The method comprises the steps of attaching a silicon layer to a substrate; integrating a semiconducting circuit in the silicon layer; forming a layered structure which includes a magnetoresistive read/inductive write head and layers of alumina on the substrate; and electrically interconnecting the semiconducting structure with the magnetoresistive read/inductive write head.
One advantage of the invention is that it provides an MR read/inductive write head assembly with ESD/EOS protection that is permanently integrated into the MR head assembly and which may be manufactured using standard photolithographic silicon processing.
Another advantage of the invention is that it provides an MR read/inductive write head assembly having a hard air bearing surface.
These and other advantages of the invention will become more readily apparent upon review of the accompanying figure and specification, including the claims.